71 350 running hot coolant backup up problem

[Stocker]

Originally Posted by Gregski

So what's next? Well I don't like how deep my flex fan sits in the fan shroud, so I picked up a 1/2 inch spacer to replace the stock spacer and move it back some.

I would throw the flex fan as far as possible and get a proper heavy duty fan clutch with a good OEM-type 7-blade fan bolted to it. That's what came on my K20 with a 350 and factory A/C. In 41 years, the only time it ran hot was when a clutch unit failed and I tried a flex fan. Didn't take me long to get rid of it and put the right one back on.

Just my 2 cents...

[Andy4639]

The fan shroud should be blocked off so that all the air pulled with the fan comes through it and not around it. The blades should be about right 50/50 but as stated a good stock fan blade will help you. Those flex fans are not for street driven vehicles and if you have AC your never going to keep it cool.
Again 180* thermastat is reading high 190's is pretty normal. It's not going to run 180* unless you do some work are buy a good aluminium radaitor.It doesn't matter what your other truck is running it has nothing to do with it.
It's a completely different vehicle.

Now if you want to swap the radiator out in both to see then yea go for it.

It wouldn't surprise me if it's the sendor for that gauge.

[Gromit]

Originally Posted by Gregski

I hear you, thanks for sharing but aint that what the tiny alan wrench is for to twist and turn the adjustable vacuum pod to adjust the vacuum to your liking, as opposed to the non adjustable OEM can which lacked that feature?

Yes but remember you are only affecting the rate of the vacuum advance portion of your total advance with that Allen trim screw. So let's say your vacuum advance will deliver up to 20 crankshaft degrees of ignition advance. You have set 12 crankshaft degrees of initial advance; so now you're POTENTIALLY up to 32 crankshaft degrees; and then your centrifugal or mechanical gives you another 24 crankshaft degrees beyond that, if you don't limit the vacuum actuator that would potentially be a total of 56 crankshaft degrees ignition advance.. way too much.

(note I have zero experience with the HEI)

I know what you are thinking and it does make sense that if you turn the Allen screw of the vacuum pot so that at your max idle 21 Hg it is only giving you a known amount of advance - but I think it is not recommended to depend on that - and I think that is why Crane also makes the adjustable stop plate and the stop plate and adjustable pot are meant to work together.

I feel bad bringing up timing if it hijacks your original overheating problem and there are such good posts already on this forum from people far more qualified than me. For example Bruce88 did a whole series on timing in his build post - starting with post #712 and it is just a masterpiece of logic.

I think if you have your initial at 12 BTDC and you are sure of your TDC and balancer mark and you set it with the vacuum advance disconnected and you know there was no centrifugal advance coming in at your 850 RPM idle that should be enough to eliminate insufficiently advanced timing as the cause of your overheating.

I guess if that is all the case and it were me I might then check to see if the heat is coming from your automatic transmission rather than the motor... assuming of course you are running the trans fluid through the factory heat exchanger in the radiator

[demian5]

Originally Posted by Gregski

so here are the results of the third test drive, this one is for all of you who suggested swapping to a 180* thermostat

180 Thermostat, running 50/50 water coolant mix, still 12 degrees initial timing

as you can see we were averaging in the high 190s, here I caught it at 199* F degrees this only proves now we are masking the problem instead of fixing it, how do I know that?, well my '74 truck is running a 180* thermostat and it operates at you guessed it 180* degrees year round

Confirm the actual temp with a temp gun or mechanical gauge instead of spending all of this money on guesses. Your new fangle gauge and sender may be off.

[demian5]

Originally Posted by Gregski

So what's next?

Confirm the actual temp with a temp gun or mechanical gauge instead of spending all of this money on guesses.

[demian5]

Originally Posted by Andy4639

It wouldn't surprise me if it's the sendor for that gauge.

See above.

[Gregski]

Originally Posted by demian5

Confirm the actual temp with a temp gun or mechanical gauge instead of spending all of this money on guesses.

These are not guesses, I am proving hypothesis, some people said its because I am running water, well I already had coolant so I tried it with 50/50, others said try a different thermostat, ok, a thermostat was only $7 bucks and a gasket was only $2 bucks, hardly any money. The $15 I spent on a new water neck was because the old one had a leak because it was pitted.

And not trying to argue with you but what exactly is a temp gun going to tell me, it will not match the temp on the gauge anyway. If I point it at the upper radiator hose it will read different, if I point at the driver metal cylinder head it will read different, if I pointed at the lower radiator hose it will read different, and different again for the intake manifold by the thermostat. So honestly and not facetiously what am I going to do with all those numbers when non of them will match my gauge.

And I know something aint right because of the lack of flow in the radiator, that's the first thing I said, it backs up.

[clay68c10]

I use those temp guns as a second opinion type of confirmation. It can just confirm that the gauge isn’t way out of whack. It should read reasonably close to the gauge when you shoot it at the metal surface by the sender.
It also can be handy to see just how well your radiator is cooling. Check the temp difference between inlet and outlet hoses and compare that to a known good vehicle. You can also find cold spots by scanning the radiator surface.
If you think the radiator has blockage, get it rodded/cored or replace it. You should be running cooler than you are.

[OBS454]

Can't see clearly but as another mentioned check the gaps between the radiator and shroud (only effective at lower speeds and idle) so that the air drawn is through the core. I remember someone telling me that those carbs are notorious for being jetted rich out of the box and that many people change the jets before even installing - maybe someone went too lean? (I run Q-jets so don't have much experience with those) Have you read the spark plugs after a run? BTW you should connect the PCV valve if you're already driving it around. Using an IR gun on the location of the temp probe would be another piece of useful information.

[Gregski]

got an update for you all that could explain why my fan is shoved so deep inside that radiator shroud, I am running a long water pump PN: 31228 so time to replace it, I belive a short snout water pump is the proper pump for these trucks, even with my short 1/2 spacer the fan still rubs against the alternator so best way to move it back is to use a short water pump and not keep piling on bandates on top of bandates

[Andy4639]

Originally Posted by Gregski

And I know something aint right because of the lack of flow in the radiator, that's the first thing I said, it backs up.

What do you mean backs up? Is the lower hose collapsing when it's running?

The temp gun will tell you if the gauge is in the ball park are not. If the gauge reads 206 and the temp gun pointed at the senor reads 190 then you know it's in the gauge.
As stated it will give you some good info on the temps at different points of motor.

[Stocker]

Temp guns are cheap enough..... can't think of a good reason not to have one.

[GASoline71]

If you switch to the correct short pump, you will need to use all the correct brackety that goes with running a short pump or your belts won't line up. You have a later model setup with the alternator on the passenger side. The short pump setup has the alternator on the drivers side.

Gary

[El Dorado Jim]

have the radiator checked for blockage or get a new one...and I don't understand why you wont check your engine with a heat gun...

[Gregski]

Originally Posted by GASoline71

If you switch to the correct short pump, you will need to use all the correct brackety that goes with running a short pump or your belts won't line up. You have a later model setup with the alternator on the passenger side. The short pump setup has the alternator on the drivers side.

Gary

Thanks Gary, yes I just found this out when I went to buy the right brackets from my Parts Pimp, lol. I enjoy learning things like this, its fun. Time to relocate accessories and make this thing right, tired of going to the Parts House and saying its a '71 but try this year for this part and that year for that part.

[Gregski]

Originally Posted by El Dorado Jim

have the radiator checked for blockage or get a new one...and I don't understand why you wont check your engine with a heat gun...

I hear you, and I will I just don't have one so I need to buy one that's all. I never said I won't do it, I was just trying to catch up to everyones advice, one step at a time.

[Gregski]

so just wanted to bring everybody up to speed on how this issue is progressing since it's a good one, by that I mean how many of us have chased an overheating issue, judging from the feedback I recon a few of us

so first, here's a very clean and efficient way I found to drain the old coolant out of the radiator without spilling a drop and making a mess

this is a Harbor Freight jobbie for stealing gas, it don't work a darn for that but works great for coolant, ha ha

[Gregski]

so I went out and bought a brand new Short Water pump, total cost $18 bucks out the door at O'Reillys

that led to swapping all the accessory brackets from the 3rd gen style (alternator on passenger side) to the 2nd gen style (alternator on the driver side)

[Gregski]

the old water pump seemed solid, and I have seen my share of perished GM water pumps, the guts on this one seemed solid, the only suspect was the weep hole below

[harpo231]

Originally Posted by Gregski

I hear you, and I will I just don't have one so I need to buy one that's all. I never said I won't do it, I was just trying to catch up to everyones advice, one step at a time.

LOL good luck wit that....i've seen folks here , up to their neck in crocodiles

[Gregski]

putting the alternator on the driver side let to moving the Power Steering Pump which led to swapping the crank pulley, but I was fine with that, as I want a period correct engine bay

so now my flex fan sits properly inside the radiator fan shroud with 50% of the blades inside the shroud and 50% out

will this fix the problem? we shall see

[Gregski]

so after she went back all together it was time to test, and to keep things fair and compare apples to apples, I put it all back to the way the General intended

FIRST TEST POST SHORT WATER PUMP SWAP

so 195* Thermostat, Short Water Pump, no bypass hose (heater core delete, remember) and running only water

RESULTS = Favorable but not there yet

the truck did not get hot idling in the garage after 15 minutes like it used to, it used to reach 205* just sitting there, I let it idle for 40 minutes and it just eventually got to 190*

so I took it for a TEST DRIVE...

and gosh darn it I saw it climb to 215* that aint right!!!

[harpo231]

You should get a bendpac to look underneath,, i don't know why you wouldn't have a bendpac

[harpo231]

[Gregski]

so for those of you suggesting for me to get the thermo gun, here it is

when the gauge read 159* this gun showed 156* pointed at the cylinder head, same on both sides, and 156* when pointed at the intake manifold by the thermostat as well

pretty similar results when the gauge was at 171* it showed like 169* on the cylinder heads

BUT...

slide that gun one inch either way on either surface and it can jump by as much as 20* or 30* so I just don't get the point because the gun readings are so inconsistent with the slightest of movements

dragging the gun across the top rubber radiator hose fluctuated the reading from like 88* to 135*